Soluble nitrocellulose and coating composition containing the same



v ment of this .ing 95% Patented Jan. 13, 1931 UNITED STATES PATENT OFF-ICE EARLE c. rrrmn, or rnmcn'rorr, NEW JERSEY, ASSIGNOR 60 E. I. DU PON'J. .DE

NEMOURS & COMPANY, or WARE 'WILMINGTON, DELAWARE, A CORPORATION OF DELA- SOLUBLE NITROOELLULOSE AND COATING COMPOSITION CONTAINING THE SAME No Drawing.

This invention relates to an improved pyroxylin coating composition and the process of preparing the same which involves the modification of the pyroxylin employed to increase its solubility in alcohol. More specifically the nitrocellulose to be employed is modified by digesting nitrocellulose of a nitrogen content not substantially over 11.5% in water at a temperature in excess of 100 C. and under pressure. The resulting product is highly soluble in alcohol and is also a subject of this invention.

One object of the invention is to produce a coating composition of high quality and high viscosity while dispensing with the use of objectionable and high priced solvents.

Another of the objects of the invention is to prepare a nitrocellulose which is substan tially completely soluble in a solvent comprisby volume ethyl alcohol. Among the advantages attending the, use of a nitrocellulose of this character in the pyroxylin" art, is the fact that ordinary denatured alcohol may be employed as a solvent. The use of a cheap. non-poisonous, readily available solvent is thus made practioaL where heretofore it has been necessary to resort to the use of solvents of high price or objectionable odor to secure complete solution of the types of nitrocellulose hitherto the most soluble.

The pyroxylins which, up to the developprocess, have had the'highest solubility. are those employed in the manufacture of plastics. This type of pyroxylin is generally about soluble in ethyl alco hol denatured with 0.5% by volume of benzol. The rapid decrease in solubility as the strength of alcohol decreases is illustrated in the following table:

Table I Per cent of nitrocellulose dissolved Strenlzth of alcohol .(per

volume) ssasa 9:00.528 N OI Application filed January 26, 1926. Serial No. 83,980.

Table I indicates clearly that there is a wide difference in the character of'the most soluble pyroxylins of the prior art which are substantially completely soluble only in 100% alcohol and only 35% soluble in 95% alcohol, and the character of the pyroxylins produced by the present process which are completely soluble in 95% alcohol.

'No special type of apparatus is required for carrying out the present process of modification. The digester may be of the ordinary type but should be capable of withstanding an internal pressure of at least pounds per square inch. It should be provided with a steam jacket and suitable safety and relief valves. Since some acidity is likely to be developed in the process, the digester should be constructed corroded by dilute nitric and at the temperatures of digestion.

In carrying the process into effect the digester is'partly filled with water and the nitrocellulose is then added. It is important to note that the pyroxyli-n should always be kept'in a wet condition to avoid danger of rapid decomposition or explosion. I prefer to use an amount of water sufficient to completely cover the nitrocellulose but a much greater amount of water is not objectionable, except, perhaps, economically. After charginsz. the digester is closed and the charge heated under pressure. The time required for completion of the operation, in general, is less the higher the temperature of discs-- tion. In this connection it may be remarked that it would appear that temperatures below 110 C. are impracticable commercially beof material not readily sulphuric acids cause of the slowness of the operation, while ing the relief valve. Digestion is continued until the product becomes more than 99% soluble in denatured alcohol containing 95% ethyl alcohol.

It will be evident that conditions of operation, materials employed, etc.,. may be- Varied within a wide range. This is illustrated in the following table, wherein are set forth the limits within which I have found the best results are obtained together with the specific conditions preferable for our purposes. It is to be understood, however, that obvious departures from the ranges therein specified to adapt our process to pe- Although denatured alcohol soluble products may be prepared from pyroxylins of lower than 10.5% nitrogen content and more than 60% initial solubility I have not included them, since their high solubility in the nitrating acids and their tendency to disintegrate during manufacture render them unfeasible as raw materials for a commercial process. Likewise, I estimate that temperatures below 110 C. are impractical commercially, merely because of the slowness of the operation and that temperatures above 140 C. are undesirable because of the danger of rapid decomposition.

The soluble nitrocellulose of my invention is substantially undergraded, as is indicated by stability tests of at least 30 minutes. These tests were made according to the German method (see Nitrocellulose Industry, lVorden, 1911, page 971). a

It also shows a viscosity of from 10 to 300 centipoises at 28 C. when tested in the form of a 6.5% nitrocellulose solution in amyl acetate.

In order to further illustrate the process by which the soluble nitrocellulose is produced, the following typical embodiments of the process are furnished:

Example A 24.2 lbs. of stabilized nitrated paper containing 30% moisture was immersed in 30 gallons of water in a 50'gallon steam jacketed digester and heated under pressure continuously for 6 hours at atemperature of 131- 134 C. The product was washed in water.

The initial and final properties were as follows:

Original Final Nitrogen content German test (minutes) Viscosity at 25 C. (6% nitrocellulose in 30% camphor-alcohol by wt.) Viscosity at 28 C. (5.5% nitrocellulose in amyl acetate) Per cent soluble in denatured alcohol (95% ethyl alcohol and 0.5% benzol) Example B 302 g. of stabilized nitrated linters con- Original Final Viscosity not rumin amyl acetate because of poor solubility- Viscosity of 6% solution 0! nitrocellulose in 30% camphor denatured v alcohol (by weight) 1589 cp. at 25 C.

The above examples indicate that the digestion must be more severe in the case of nitrated linters than in the case of nitrated a er.

p n the above examples 95% ethyl alcohol containing 0.5% benzol was employed as the solvent of the product in both cases, Tests have indicated, however, that the presence of 0.5% benzol as a denaturant in 95% by volume ethyl alcohol has so slight an eflect on the solubility of the nitrocellulose as to be negligible for all practical purposes.

In all cases the solubility of the nitrocellulose in alchohol was determined by the following method: Shake 1 gram nitrocellulose in 200 cc. of alcohol for two hours. Filter on a weighed Gooch. Dry Gooch and determine the weight of the insoluble residue. The excess of alcohol is so great that it can be as-. sumed the portion of nitrocellulose insoluble in it would not be dissolved in any amount of alcohol of the same concentration.

The soluble nitrocellulose is peculiarly adapted for incorporation into a pyroxylin enamel or lacquer. By reason of its extreme solubility in ethyl alcohol it is possible to employ ordinary denatured alcohol in place of more expensive or otherwise objectionable solvents heretofore used in the preparation of such compositions.

In order to present in detail the nature of the improved coating compositions made from the. solubilized nitrocellulose, typical examples are given below. It is to be understood that these are entirely illustrative of the invention.

Following is an example of a coating composition in which the use of alcohol-soluble nitrocellulose makes it possible to eliminate ethyl acetate:

Ewample 0 Prior art New Per cent Per cent Pyroxylin (12% N) 10 Pyroxylin (soluble in 95% alcohol) 14 Castor oil 20. 28

Pigment 10 14 Ethyl acetate l5 Benzol 30 30 Denatured alcohol (95% by vol.) 15 14 An example of a high solids enamel of the new type is giyen below. It will be noted that the ethyl acetate of the prior art enamel has been replaced by ethyl alcohol and the butyl acetate by diethyl carbonate, making the odor of the new type enamel unobjectionable for interior use:

Example D The compositions given above .are on the basis of spraying consistency. The proportion of pigment will, of course, vary according to the hiding power and other properties of the pigment, beingas low as two parts in the case of some black enamels and as high as 25 parts forsome light colors, such as whites. The use of pyroxylin soluble in denatured alcohol is also of advantage in the so-called mixing lacquers, which are solutions of nitrocellulose, usually in'cheap solvents, added to solutions of shellac in such a solvent as denatured alcohol. The purpose of introducing theanitrocellulose is to waterproof the shellac, which is well known-to be highly permeable to water.

.. Following are illustrations of the use of alcohol-soluble nitrocellulose in mixing lacquers.

In order to eli'ect the waterproofing of the shellac, mix 100 parts of the prior art lacquer, or parts of the new type of lacquer, with 100 parts of a solution of 30% by weight of I shellac in ethyl alcohol denatured with 10% methyl alcohol. In addition to the saving enabled by the use of a cheaper solvent mixture the higher solids content of the new lacquer at the same Viscosity reduces the total amount of solvent which must be evaporated to deposit a given weight of coating.

Tests have shown the films produced b the coating composition in which the mo ified nitrocellulose and denatured alcohol are employed to be equal in quality, viscosity and durability to those produced from the unmodified types of nitrocellulose with the more expensive and objectionable solvents formerly employed.

I claim;

1. The method of treating cellulose nitrate comprising digesting cellulose nitrate at. elevated pressure in a non-solvent, inert liquid at a temperature above 100 C. and below the decomposition point of the cellulose nitrate, and stabilizing the product by washing with water.

2. The method of treating cellulose nitrate comprising digesting cellulose nitrate in Water at'a temperature between C. and 140 C. at a pressure above atmospheric and below about 50 pounds per square inch and ;washing with water to produce a stability of thirty minutes. (German test).

3. A cellulose nitrate of reduced viscosity having a nitrogen content of at least 10% and less than 11.5% and being substantially completely soluble in 95% ethyl alcohol and having a stability of thirty minutes (German test 4. A cellulose nitrate of showing a stability of atleast 30 minutes (German test) and being more than 99% soluble in 95% ethyl alcohol. 7

J 5. The method of making a cellulose nitrate having about 99% solubility in 95% ethyl alcohol comprising digesting cellulose nitrate having a nitrogen content between about 10% and 11.5% in aninert non-solvent reduced viscosity liquid at pressure above atmospheric and at a temperature above C. but below the decomposition point of the cellulose nitrate and washing with water until the product is stable.

6. The method of making a cellulose nitrate having 99% solubility in 95% ,ethyl alcohol comprising digesting cellulose nitrate having a nitrogen content between about 10% and 11.5% in water at pressure above atmospheric but less than about 50 pounds per square inch and at a temperature between C. and C. until 99% solubility in 95% ethyl alcohol is obtained and stabilizing by washing with water until the product will give a German tcst upward of about thirty minutes.

7. The method of making a cellulose nitrate having 99% solubility in 95% ethyl alcohol comprising digesting a cellulose nitratehaving a nitrogen content between about 10% and 11.5% in water at a pressure of about 20-40 pounds per square inch, andatatemperature between 100 C. and 140 C. and in stabilizing the digested cellulose nitrate by washing with wateruntil it will give a German test of at least thirty minutes.

8. A coating composition comprising a solution of a cellulose nitrate of reduced viscosity having a nitrogen content between 10% and 11.5%, a stability of thirty minutes (German test), and which is substantially completely soluble in 95% ethyl alcohol.

In testimony whereof I aflix my signature.

EARLE C. PITMAN. 

